Partial dyeing of fur skins and leather



nited States Patent PARTIAL DYEING OF FUR SKINS AND LEATHER Otto Markgraf, Neckargemund, Curt Schuster, Karl Herrle, and Ernst Boehm, Ludwigshafen (Rhine), and Erhard Schaefer, Mannheim, Germany, assignors to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany 'No Drawing. Filed May 21, 1957, Ser. No. 660,460

Claims priority, application Germany May 25, 1956 6 Claims. (Cl. 8-10) This invention relates to a process for the partial dyeing of fur skins and leather with the use of polymers which dissolve in cold water but not in hot dyebaths.

It is already known that the hair of fur skins can be partially dyed by reserving the tips of the hair with paraffin wax or thickening agents. The application and removal of these reserving agents is troublesome. The solvents necessary for said removal moreover often impair the shade of colour and the handle of the leather. it is also already known that fur skins can be provided with a mixture dyeing by precipitating lead sulfide on the hair and partially converting this into lead sulfate by oxidation with hydrogen peroxide. Apart from the fact that only grey-white shades can be achieved by this method, the white parts become yellow in time.

The object of this invention is a process for the partial dyeing of fur skins and leather according to which there is used as a reserving agent a polymer which does not impair the dyeing process and can readily be removed again after the dyeing.

The object of the invention is achieved by covering those parts of the fur skins or leather which it is desired not to dye with a polymer of a N-vinyl lactam which is soluble in water at room temperature but insoluble at elevated temperature, and then carrying out the dyeing in a bath the temperature of which maintains the polymer in the insoluble state.

Polymers of N-vinyl lactams which are water-soluble at room temperature and water-insoluble at elevated temperature are obtained by polymerisation of N-vinyl lactams as such or in admixture with other polymerisable compounds by conventional polymerisation methods, for example with azo-isobutyronitrile as polymerisation catalyst.

As polymers there come into question especially those of N-vinyl lactams which contain at least eight carbon atoms in the molecule.

To this group belong polymers of vinyl caprolactam and also its copolymers with vinyl pyrrolidone, vinyl methyl ether or vinyl caprylic lactam. The K-value may be from 20 to 60. The proportion of vinyl caprolactam in the copolymer may be as low as 20 percent by weight, with reference to the copolymer. Other suitable polymers are for example poly-N-vinyl-C-ethylpyrrolidone or copolymers of vinyl caprylic lactam and vinyl pyrrolidone or of vinyl pyrrolidone and acrylic acid esters or vinyl esters. aliphatic carboxylic acids and alcohols respectively with from 1 to 4 carbon atoms in the molecule.

The said and similar polymers are soluble in cold water but are insoluble in hotter water. The temperature at Which the polymer passes into the insoluble state may be These esters can-be derived from rather sharply defined, but in each case is dependent on For example poly- (1932), p. 58), is insoluble in water at about 36 to 40 C. but soluble in water at room temperature.

The terms solubility and insolubility may be explained by the following experimental results, without thereby defining any limits: up to 150 grams of polyvinyl caprolactam will dissolve in millilitres of water at 20 C. If a solution of 10 grams of polyvinyl caprolactam in 100 millilitres of Water prepared at 20 C. be heated to 40 C., 99.7 percent of the polymer are precipitated. Upon cooling, the precipitate again goes completely into solution. If the solution prepared at 20 C. contains 20 grams of polyvinyl caprolactam in 100 millilitres of water, then 97.5 percent of the polymer is precipitated at 40 C.

The preparation of polymers which are already waterinsoluble at 30 C. by the use of a N-vinyl lactam will present no difficulty to the expert in the polymerisation field. To a certain extent, the temperature range in which the polymers are water-insoluble or water-soluble can be varied by the addition of salts to the dyebath or to the washing water.

Of the available polymerisable compounds from which the polymers suitable for the partial dyeing of fur skins and leather according to this invention can be prepared, some examples are given by way of explanation and not by way of limitation of the invention, in the following tables:

I II

N-vinyl caprolactam. vinyl methyl ether. N-vinyl caprylic laetam. vinyl propyl ether.

N-viuyl-O-ethyl-pyrrolidone.

acrylic acid esters. (N-vinyl-pyrrolidone).

methaerylic acid esters.

The compounds specified under I can be polymerised alone, or mixed with each other, or together with one or more of the compounds specified under II. In the'latter case, the proportion of compound specified under I should not amount to less than 20 percent by Weight with reference to the copolymer. N-vinyl-pyrrolidone alone is not suitable but when polymerised together with the other compounds specified under I or together with acrylic acid ester or vinyl ester, it also yields polymers suitable for the purpose of the present invention. The acrylic acid and methacrylic acid esters can be those of alcohols with from 1 to 4 carbon atoms in the molecule, i.e. of methyl and ethyl alcohol and the propyl and butyl alcohols. The vinyl esters can be those of carboxylic acids with from 1 to 4 carbon atoms, such as formic acid, acetic acid, propionic acid and butyric acid.

Mixtures of polymers of the compounds specified under I and for example, polyvinyl methyl ether, watersoluble derivatives of cellulose, such as starch, degraded starch, carboxymethylcellulose, alginates, tragacanth or albuminous substances, such as casein, may also be used. In these mixtures, the polymer of the compounds specified under I should not amount to less than 40 percent by weight with reference to the weight of the total mixture. Mixtures of at least 40 percent by weight of polymers of any of the compounds listed under I with dispersions of polymers, for example of polystyrene, polyvinyl chloride, polyacrylic acid esters and polyvinyl esters or of copolymers of the said polymers can also be used; The percentage indicated refers to the overall quantity of the polymer which is soluble in water at room temperature and the dispersed polymer. The dispersing agent may be water or a mixture of water and a liquid miscible with water. In practice it Was found that upon washing the skin or leather the said dispersions are not dissolved but detached together with the water-soluble polymers.

The polymers are applied to the fur skins or leather in aqueous, aqueous-organic or organic solution, preferably in concentrations of to 50 percent, by spraying, brushing, painting or printing. By organic solution we mean herein a solution'in an organic solvent which is miscible with Water, as for example methyl alcohol, ethyl alcohol, isopropyl alcohol or acetone. The amount of polymer to. be applied to the fur skin or leather depends on the nature of the material to be dyed. The hair of fur skins should in general be reserved with a layer 1 to 3 millimetres thick in order that no dyestuff will diffuse through during dyeing. The thickness of the hair of the fur skin determines whether a more highly or less concentrated solution is to be used, i.e whether the polymer solution is to be more or less diluted, or whether the solution is to be applied once or several times in order to. make the sheathing sufficiently thick. For example in the case of a fine woolly skin, 200 to 400 grams of a polyvinyl caprolactam of the K-value S0 to 60 is sufficient for 1 square metre, but in the case of a kempy skin 100 grams may be sufiicient whereas in the case of a dense sheepskin 600 grams may be necessary. It has proved to be preferable to adjust the polymer solution intended for application to such a concentration that the viscosity of the solution favours the formation of a well-adhering film. A viscosity is preferred with which the outflow time from a Ford beaker DIN 53211 with a 4 millimetre nozzle open ing amounts to to 60 (a viscosity of about 50 to 300 cps. determined by means of a Drage-type structure viscosimeter STV) seconds or more. If the solution is sprayed on, it should have a lower viscosity, for example it may have an outflow time of 19 seconds (a viscosity of about 80 cps). If it is brushed on, its outflow time may amount to 60 seconds and for printing, for example, 90 to 100 seconds (a viscosity of about 400 to 5.00. cps).

By drying at ordinary or elevated temperature, for example 40 to 60 C., the reservation becomes directly solid andnon-sticky. The polymers of N-vinyl lactams used for the reservation are insensitive to the temperatures permissible in the drying of fur skins and leather, is. the property of the polymers of being insoluble in water at elevated temperature and soluble in water at lower temperature is not influenced by the drying temperature.

The dyeing of the fur skin or leather reserved with the said polymers is carried out by the usual methods and for the usual times, but the temperature of the dyebath must be high enough to prevent the polymer from being dissolved. There may be used for dyeing all dyestuffs which are customary in the fur skin and leather dyeworks and which can be dyed at temperatures at which the polymers are water-insoluble. Among such dyestuffs are wool dyestuffs to which belongs the group of azo dyestuffs such as acid dyestuffs, complex metal dyestufis, dispersion dyestufls. Vat dyestufis, such as indigo, and substantive dyestuifs and oxidation dyestuffs are further classes which are usual in the dyeing of fur skins and leather and which also can be used in the process according to this invention. The usual dyeing auxiliaries, as for example Glaubers salt, acids, vatting agents, hydrogenperoxide and levelling agents, can be co-employed without danger for the reservation.

After the dyeing, the reservation is removed by simple washing with sufliciently cold water. Auxiliaries, as for example fatty alcohol sulfonates, or non-ionogenic washing and cleansing agents, may be contained in the washing water.

On natural white skins there may be produced in the said manner colour effects such as are to be found in multicoloured, partially coloured skins, of natural origin, as for example seal, ocelot, chinchilla and the like. The for skin may also be dyed first in a pale shade without reservation and then in a darker shade after reservation, or conversely dyed a dark shade after reservatiq and then after washing off the reservation, provided with another dyeing on the remainder.

Leather can be dyed on one side by the said process, instead of by the brushing method as hitherto, in the vat by reserving, for example, the flesh side. In this vat a faster dyeing is obtained. By simple covering of parts of the grain or flesh side with the polymers, patterns or antique leather designs may also be dyed on. The leather may also be dyed differently on the two sides by reserving one side and dyeing the second side, and thereafter dyeing the first side, if desired after reserving the second side.

The type of tanning of the skin material and leather which can be partly dyed according to this invention is without importance per se, but one of the known tanning methods must have been used which leads to a shrinkage temperature which lies above the dyeing temperature so that the leather is not damaged. There may be mentioned chrome-tanned, formaldehyde-tanned and oiltanned fur skins or leather, the shrinkage temperature of which lies for example at 70 to C.

The advantage of our invention resides in the fact that fur skins and leather can be dyed partially by coating the material to be dyed with a reserving agent from an aqueous solution or a solution miscible with water, drying the coating so prepared, dyeing it under ordinary cohditions in adyebath which does not fall below a certain temperature and washing the material so dyed in water at room temperature whereby the polymer applied for reserving purposes is removed leaving undyed places.

The following examples will further illustrate this invention but the invention is not restricted to these examples. The parts specified are parts by weight.

Example I A natural lambskin (for example a Tuscany lambskin) has brushed onto it through a stencil, which has the design for example of a sealskin, a 10 to 20 percent aqueous or alcoholic solution of poly-N-vinyl caprolactam. The skin is allowed to dry and is dyed at 50 C., for example with one or more dispersion dyestuffs, which are described for example in Schultz, Farbstofftabellen, volume II, page 75, 1934 edition.

The polyvinylcaprolactam is dissolved away from the skin by washing the dyed piece in cold water. The reserved places remain uncoloured. The same effect is obtained with acid dyestuffs or vat dyestuffs.

Example 2 An aqueous or aqueous-alcoholic solution of a copolymer of 90 parts of N-vinylcaprolactam and 10 parts of vinylcaprylic lactam is sprayed onto a white rabbit skin which is then dried, dyed with oxidation dyestuffs at 45 C. and Wflfihfid with cold water. The tips of the hairs are undyed.

Example 3 Leather, of which the flesh side has been covered with a 20 to 30 percent solution of poly-N-vinyl-caprolactam by spraying, is dyed hot in the vat with acid or substantive dyestuffs and washed well with cold water. The flesh side remains undyed.

Example 4 The grain side of a leather is printed with a 30 to 50 percent solution of the copolymer used in Example 2, dried and dyed at 60 C. with any leather dyestulf. The copolymer is removed by washing with cold water. The printed places remain undyed.

Example 5 40 parts of polyvinyl caprolactam and 60 parts of polyvinyl methyl ether are stirred with such an amount of water that the outflow time in a Ford beaker amounts to 50 seconds (a viscosity of about 250 cps.). This o ution is. prayed or b ushed onto a So th American lambskin (Lincoln lambskin) so that the tips of the hair or flocks are sheathed in a thickness of about 2 millimetres. After drying at a temperature of about 40 C., the skin, without preliminary wetting, is dyed directly in a dyebath the temperature of which is regulated at 55 C. Dyeing may be carried out for example with a vat dyestuff for wool from the chloranil series for about 45 minutes by the prescription known for wool dyeing. After washing, and developing the dyestufl, which is carried out at a temperature above the coagulation point of the polymer mixture, the skin is washed with water at 25 C., if desired with the addition of a washing agent, to remove the polymer. The polymer used for the reservation is removed after about to minutes if the material is kept in motion.

Example 6 A mixture of 50 parts of polyvinylcaprolactam and 100 parts of a 50 percent polystyrene dispersion, or a mixture of 70 parts of polyvinyl caprolactam and 60 parts of a 50 percent polyvinylpropionate dispersion, or a mixture of 70 parts of polyvinylcaprolactam and 60 parts of a 50 percent dispersion of a copolymer of 75 percent of methyl acrylate and percent of butyl acrylate, or a mixture of 60 parts of polyvinylcapro-v lactam and 40 parts of the sodium salt of carboxymethylcellulose in 100 to 200 parts of water is applied to the tips of the skin of a Portuguese milk lamb or printed in certain places. After drying, it is dyed with an acid dyestuff, for example the dyestuff obtained by diazotizing l,4-aminonaphthalene-sulfonic acid, coupling with alphanaphthalene sulfonic acid, diazotizing and coupling this with betahydroxynaphthalene in the manner usual for W001 with an addition of Glaubers salt and acid, for 1 hour at 60 C. After washing out the polymer with cold water, if desired with the use of a washing agent, entirely undyed places remain.

What we claim is:

1. A process for the partial dyeing of fur skins and leather with dyestuffs for fur skin and leather which process comprises partially covering the material to be dyed selected from the group consisting of fur skins and leather with a polymer which has been prepared from at least 20% by weight, with reference to the weight of total polymer, of a N-vinyl lactam having at least 8 carbon atoms in the molecule, which polymer is insoluble at elevated dyebath temperatures and soluble at lower temperatures, drying the thus partially covered material to be dyed, dyeing the same at a temperature sufiiciently high to keep the polymer in the water-insoluble state, and washing the dyed material in an aqueous bath at a temperature at which the applied polymer is soluble to remove said polymer and thus obtain the partially dyed product.

2. A process for the partial dyeing of fur skins and leather as claimed in claim 1 wherein the material to be dyed is partially covered with a polymer which has a K-value of 20 to and which has been prepared from at least 20 percent by weight with reference to the total polymer, of a N-vinyl lactam containing at least 8 carbon atoms in the molecule, and dyeing is carried out at temperatures above 40 C.

3. A process for the partial dyeing of fur skins and leather as claimed in claim 2 wherein there is used for the partial covering step a mixture which contains (a) a polymer prepared from a N-vinyl lactam having at least 8 carbon atoms in the molecule and (b) a polymer of a polymerisable monomer selected from the class consisting of a vinyl ether, an acrylic ester, 21 methacrylic ester, N-vinyl pyrrolidone, vinyl-chloride and styrene.

4. A process for the partial dyeing of fur skins and leather as claimed in claim 2 wherein there is used for the partial covering step a mixture Which contains (a) a polymer prepared from a N-vinyl lactam having at least 8 carbon atoms in the molecule in an amount of at least 40 percent by weight and (b) a high molecular product on a natural basis selected from the group consisting of starch, carboxymethyl cellulose and casein.

5. A process for the partial dyeing of fur skin and leather with dyestuffs capable of dyeing fur skins and leather, which process comprises: first partially and selectively covering the material to be dyed selected from the group consisting of fur skins and leather with a polymer of at least 20% by weight, with reference to the weight of total polymer, of N-vinyl caprolactam, which polymer is insoluble at elevated dyebath temperatures and soluble at lower temperatures, drying the thus partially covered material, then dyeing said partially covered material at a temperature sufficiently high to keep the polymer coating in the water-insoluble state, and washing the dyed material in an aqueous bath at a temperature at which the applied polymer is soluble to tomove said polymer and thus obtain the partially dyed product.

6. A process as claimed in claim 5, wherein the polymer is poly-N-vinyl caprolactam.

References (Cited in the file of this patent UNITED STATES PATENTS 2,769,684 Geigy Nov. 6, 1956 2,802,714 Olpin Aug. 13, 1957 FOREIGN PATENTS 759,595 Great Britain Oct. 24, 1956 OTHER REFERENCES Schildknecht: Vinyl and Related Polymers, pp. 6, 777, John Wiley and Sons, Inc., New York, Feb. 20, 1952. 

1. A PROCESS FOR THE PARTIAL DYEING OF FUR SKINS AND LEATHER WITH DYEWSTUFFS FOR FUR SKIN AND LEATHER WHICH PROCESS COMPRISES PARTIALLY COVERING THE MATERIAL TO BE DYED SELECTED FROM THE GROUP CONSISTING OF FUR SKINS AND LEATHER WITH A POLYMER WHICH HAS BEN PREPARED FROM AT LEAST 20% BY WEIGHT WITH REFRENCE TO THE WEIGHT OF TOTAL POLYMER, OF A N-VUNYL LACTAM HAVING AT LEAST 8 CARBON ATOMS IN THE MOLECULE, WHICH POLYMER IS INSOLUBLE AT ELEVATED DYEBATH TEMPERATURES AND SOLUBLE AT LOWER TEMPERATIRES, DRYING THE THUS PARTIALLY COVERED MATERIAL TO BE DYED, THE SAME AT A TEMPERATURE SUFFIEIENTLY HIGH TO KEEP THE POLYMER IN THE WATER-INSOULBLE STATE, AND WASHING THE DYED MATERIAL IN AN AQUEOUS BATH AT A TEMPERATURE AT WICH THE APPLIED POLYMER IS SOLUBLE TO REMOVE SAID POLYMER AND THUS OBTAIN THE PARTIALLY DYED PRODUCT. 